CNN — (CNN) -- Sybrina Fulton, Trayvon Martin's mother, did not hesitate when asked Friday whether the voice heard screaming for help on a 911 call made the night her son died was his.

"Absolutely," she answered resolutely.

Identifying that panicked voice is considered key to proving whether George Zimmerman or Martin was the aggressor the night of February 26, 2012, when the 17-year-old Martin was shot and killed.

It was the first time in Zimmerman's second-degree murder trial that a member of Martin's family took the stand, and it occurred as the prosecution rested its case and the defense began presenting its own -- calling Zimmerman's mother, Gladys, as its first witness.

Friday's developments added more detail, and emotion, to a saga that gained national attention on guns laws and race in America -- in part due to allegations that Zimmerman, who is Hispanic, targeted Martin, who is African-American.

Earlier Friday, prosecutor Bernie de la Rionda played the 911 call while a stoic Fulton listened. When asked whether she recognized the screaming voice, the mother -- who earlier stated that her son was "in heaven" -- said it was that of "Trayvon Benjamin Martin."

While brief, Fulton's testimony reinforced the prosecution's contention that Martin did not pose a threat to Zimmerman when the former neighborhood watch captain shot and killed him. Zimmerman has pleaded not guilty and claimed he shot the teenager in self-defense.

Defense attorney Mark O'Mara asked Fulton, "As his mother, there was no doubt it was him screaming?" to which she replied, "Absolutely."

O'Mara then attempted to raise the possibility that Zimmerman was not to blame for her son's death. "You certainly hope, as a mom, that your son Trayvon Martin would not have done anything that led to his death, correct?" he asked.

"What I hoped for," said Fulton, "is that nothing happened and he'd still be here. That's my hope."

Jahvaris Fulton, Martin's older brother, also testified Friday morning about the voice on the 911 call and confirmed his certainty that it belonged to his brother. The 22-year-old college student added that he had "heard him (Martin) yell" before, but "not like that."

He testified that when he first heard the call, he thought it was his brother's voice but wasn't sure. "I guess I didn't want to believe it was him," Jahvaris told O'Mara. "I was clouded by shock and sadness."

Judge Debra Nelson denied a request by O'Mara to play a 2012 TV interview during which Jahvaris Fulton said he wasn't sure whether the screams were those of Martin.

In that interview, Jahvaris said, "I would think it was my brother, but I am not completely positive that it is him." Yet Judge Nelson ruled Jahvaris' testimony matches what he said in that interview, so jurors would not hear it.

The court also focused again on specifics of the shot that killed Martin, and what it could reveal about the fatal struggle between him and Zimmerman.

Voluscia and Seminole County associate medical examiner Bao Shiping testified about the autopsy he performed on Martin, saying the muzzle of Zimmerman's gun was likely in loose contact with Martin's clothing, indicating the teen was shot at close range.

In testimony that at times turned contentious, Bao also said Martin did not die right away after the gunshot.

"I believe he was alive for one to 10 minutes after he was shot. His heart was bleeding until there was no blood left," the medical examiner said as autopsy photos lingered on a courtroom screen, adding that Martin was "suffering (and) in pain."

"There is no chance he could survive. Zero."

During a contentious cross-examination, lawyer Don West expressed doubts about the condition of Martin's body and clothing when it was examined, noting the victim was not moved from the scene for about three hours. Bao would not confirm that timeline-- despite West's repeated attempts to have him do so -- because he said he was not there.

As the two disputed Bao's ability to establish a timeline, Judge Nelson interjected, telling the witness to "please stop speaking so Mr. West can ask the next question."

Prepared notes that Bao was reading from also drew West's attention. When asked about them, Bao said, "I typed out potential answers to your potential questions."

Bao objected to sharing his notes, telling the judge that they were private and no one had seen them.

Despite his protests, Nelson allowed the papers to be copied and reviewed by lawyers from both sides.

The notes revealed that Bao had changed his mind about a couple of issues: the amount of time Martin survived after being shot and whether the marijuana in the teenager's system was enough to affect him.

West argued that the prosecution knew about these changes but didn't tell the defense. But Bao insisted that he did not tell anyone that he'd changed his opinion.

The defense attorney pressed Bao, too, on the collection of Martin's clothes and scraping of his fingernails. The medical examiner, though, said he couldn't remember each detail and that he'd trusted that his technicians properly followed procedures.

Late in Friday's court proceedings, O'Mara made his pitch for acquittal -- arguing that Zimmerman acted in self-defense; there was no direct evidence of ill will, hatred or spite surrounding Martin's killing; and that it was still unclear who could be heard screaming on the 911 call.

There is "no other reasonable hypothesis" for what happened, the defense attorney argued, besides self-defense.

The judge, though, denied the motion for acquittal. Shortly thereafter, about 5 p.m., the prosecution formally rested its case and the defense began its own.